Video storage tubes



Sept. 23, 1958 HE 2,853,648

Y VIDEO STORAGE TUBES I Filed June 29, 1953 PU LSE GENERATOR COLLECTORFIELD-FORMING ELECTRODE 1 ELECTRODE 3 (TARGET) 4 (CHARGE-STORAGESURFACE) 5 (SIGNAL PLATE) LIGHT SOURCE LINE SCAN 13 OIL FRAME SCAN c0| A22 COMBINED COLLECTOR a FIELD-FORMING PULSE A 25 ELECTRODE.

GENERATOR 3 (TARGET) (cHAR0E-sT0RAcE suRFAcE) 5(SIGNAL PLATE) R N 6FRAME SCAN COIL 16 A FOCUS COIL {5 58% souRcE' 12 /8 Aliorney storagesurface.

r 2,853,648 Patented Sept. 23, 1958 2,853,648 VIDEO STORAGE TUBESRichard Theile, Marburg (Lahn), Germany, assignor to Pye Limited,Cambridge, England, a British company Application June 29, 1953, SerialNo. 364,543

9 Claims. (Cl. 315-11) The present invention relates to televisionpick-up tube arrangements incorporating a video storage tubeof the kindemploying high-velocity electron scanning, such as those of the typeknown as iconoscopes and image iconoscopes and to a method of operatingthe same for producing a video signal whereby an improved performance isobtained.

Tubes of this kind essentially comprise a target having a storagesurface backed by an electrode termed a signal plate, the storagesurface being capable of carrying a charge pattern corresponding to thepoint-by-point brightness values of a light image focused on the tube.In the case of tubes of the image iconoscope type, the storage surfaceis secondary-emitting and the tube has a photo-cathode upon which thelight image is focused and which, in response thereto, releasesphoto-electrons which are accelerated and focused on to the storagesurface of the target to form the charge pattern by secondary emissionfrom the storage surface. In the case of tubes of the iconoscope type,the storage surface is a photosensitive mosaic upon which the lightimage is. focused to form the charge'pattern by photo-emission from thein either case, the charge pattern on the storage surface is evaluatedby a high-velocity scanning beam of electrons the efiectof which is togenerate a train of signal pulses in the signal plate which constitutethe output video signal of the tube; A collector electrode arranged inthe tube near the storage surface collects electrons emitted from thestorage surface under the action of the incident photo-electrons, in thecase of the image iconoscope, or the incident light in the case of theiconoscope, and under the action of the scanning beam. In'the normaloperation of such tubes, the storage surface is restored at eachscanning operation to an equilibrium potential from which the chargestorage process starts at each point of the storage surface inaccordance with the light value of the corresponding pointof the lightimage. High-velocity electron scanning as employed in such tubespromoteslthe emission of secondary electrons from the storage surface inexcess of unity ratio to the number of primary bombarding electrons andunder these conditions the storage surface assumes operating eration ofspurious signals, production of the visible effect known as flare in thereconstituted pictures, and

lack of average brightness components in the generated video signal. 7

' It has previously been proposed to minimize the effects of theabove-mentioned disadvantages by providing a method and apparatus forproducing a video signalutilizing a video storage tube of the kinddescribed in which the operating point of the storage surface ismodified.

This was effected by submitting the storage surface of the tube,periodically during the'flyback periods of the v with remedying thisdisadvantage in tubes of the im Scanning beam and preferably during theframe-flybac k 2 periods, to the simultaneous and combined actions of anelectron irradiation, causing the storage surface to emit electrons, andof a field causing the emitted electrons to return to the storagesurface so as to cause the storage surface to be charged negativelyrelatively to its normal equilibrium potential, that is, to the normalcollector potential, whereby the equilibrium potential or averageequilibrium potential of the storage surface was changed from that whichit would normally attain during the fiyback periods, thus modifying theoperating point of the tube. In particular, with a tube of the imageiconoscope type this prior proposal suggested the irradiation of thestorage surface with a pulse of high-velocity diffuse electrons to causethe surface to emit secondary electrons, the pulse of irradiatingelectrons being generated for example by illuminating the ordinaryphotocathode of the tube With a pulse of diffuse light. case of tubes ofthe normal iconoscope type, the suggestion was to bombard thephoto-sensitive storage surface thereof directly with a pulse of diffuseelectrons in order to obtain the required potential shift. With bothkinds of tube, the required field for returning the emitted electrons tothe storage surface was obtained by means applying either a suitablenegative voltage pulse to the collector electrode or a positive pulse tothe signal plate while the irradiation ofthe storage surface wasproceeding. These proposals are contained in United States LettersPatent No. 2,651,674, filed May 8, 1950, in the name of Richard Theileand entitled Television Transmission From Intermittent Film By Means ofPulsed Pick-Up Tube and United States Letters Patent No. 2,733,292,filed May 8, 1950, in the names of John E. Cope and Richard Theile andentitled System for Correcting the Equilibrium Potential of StorageTubes. In;

these proposals it was also arranged that both the electron irradiationpulses and the voltage pulse should be of the samev duration and shouldnot be of longer duration than the flyoack period during which they areapplied. If necessary, blanking pulses were simultaneously applied to asignal amplifier connected to the output of the tube in order to avoidoverloading and transient eifects.

Although successful in many directions, tubes of the improved kind,mentioned above, do, however, suffer from the disadvantage of anon-uniform accumulation of the charge in the flooding period which isparticularly manifested at the centre of the charge storage surfacewhich accumulates most of the charge, this accumulation appearing as ashaded background in the centre of the viewed picture. This effect hasbeen understood to be caused by the secondary emission process involvedsince, as the field between the signal plate and the collector electordeof the tube is not uniform, the slow secondaries being returned aredeflected by the non-uniformity of the field in such a manner as toaccumulate most charge at the centre of the screen.

The. present invention is more specifically concerned proved kindreferred to.

According to the invention, there is provided a television pick-up tubearrangement of the kind referred,

to, comprising means for modifying the field between the storage surfaceand the collector electrode to render and/ or disposing the collectorelectrode so as to produce an appropriate field between the signal plateand the cola. lector electrode. I

The preferred embodiment comprises the division of In the the collectorelectrode into a plurality of sections, and applying to the severalsections negative voltage pulses of differing amplitudes, and incarrying this embodirnent of the invention into effect, the collectorelectrode sections may be connected to a common pulse generator througha VolEage dividing arrangement so adjusted as to produce a plurality ofoutput pulses of differing amplitudes.

In a preferred arrangement, the collector electrode is divided into twosections, and the voltage divider may comprise a pair of resistorshaving differing values connected in parallel to the output of a pulsegenerator ar ranged to produce a negative pulse of adjustable amplitudewhereby negative pulses of differing but constant amplitudes areprovided to the sections of the collector electrode.

Preferably the resistors are variable resistors so that the amplitudesof the negative pulses applied to the appropriate sections of thecollector electrode may be varied at will to give' more positivecontrol.

If desired, one or more of the collector electrodes may be fed with aslightly positive pulse to produce a control, the effect of which can beprecisely and easily graduated.

In a modification, instead of sub-dividing the collector electrode, thatelectrode may have its normal shape and/ or disposition varied to bringabout the effects required. For example, the collector electrode, whichis normally in the form of an annular ring, formed from strip material,may be formed from material having a non-planar section arranged toproduce fields in conjunction with a signal plate that evens out theelectron flow in the space between the two electrodes.

Alternatively, the collector electrode ring or a portion thereof may bearranged as a section of a cone so as to produce field effectscalculated to influence the redistribution of the secondary electrons inthe manner aforementioned.

If desired all these expedients mentioned may be provided together.

In order that the invention may be more clearly understood, referencewill now be made to the accompanying drawings which show two specificembodiments thereof by way of example and in which Fig. 1 ShOWs a tubehaving a divided collector electrode, and

Fig. 2 shows a tube having a single collector electrode suitably shapedso as to produce field effects calculated to influence theredistribution of the secondary electrons in a substantially even mannerover the surface of the charge storage plate.

In Fig. 1, the pick-up tube comprises an evacuated glass envelope 1having a photo-cathode 2' at one end thereof and a target 3 at the otherend thereof comprising a charge-storage surface 4 and a signal plate 5,which latter is connected by a lead 6'to a load resistance 7 grounded at8, the output of the tube being taken across said resistance 7 andamplified in a suitable amplifier, such as tube 9.

The charge-storage surface 4'is arranged to be scanned by means of anelectron gun schematically illustrated at 10, the beam from the gun 10being focussed by focus' coil 11 connected to a suitable source ofpotential schematically illustrated at 1 2, suitable deflection coilsfor the beam being shown at 13 and 14 for causing the beam to scan inhorizontal and vertical directions in known manner. The deflection coils13, 14 are connected to appropriate waveform generators 15, 16 inaccordance with known practice. The source 12 and the generators 15 and16 are of a type very well-known in the art and therefore need not bedescribed here.

As is usual in such tubes, a collector electrode is pro-' vided at 17and this electrode is held at a positive potential with respect to thecathode 10, asschematically illustrated by potential source 18. Thecollector electrode collects the secondary electrons emitted from thecharge storage surface 4 under the influence of the light image from thephoto-cathode 2.

In the prior proposal employing the negative pulsing technique referredto above, means are provided for periodically pulsing the photocathode 2with diffuse light from a light source during the frame flyback periodand simultaneously with this pulsing the collector electrode is providedwith a negative pulse so that a field is produced to cause the electronsemitted from the storage surface to be returned thereto to charge thestorage surface negatively relatively to its normal equilibriumpotential, that is to the normal collector potential, whereby theequilibrium potential or average equilibrium potential of the storagesurface is changed from that which it would normally attain during theflyback periods thus modifying the operating point of the tube.

A similar arrangement is illustrated in Fig. 1 in which there is shownschematically a light source 19 which is arranged to be pulsed on by apulse generator 20 during the frame flyback period of the tube forproducing the effect mentioned above. According to the first embodimentof the present invention, the collector is divided into two discretesections and both the main collector electrode 17 and the subsidiarycollector electrode 21 are given negative pulses during the frameflyback period, the pulses being supplied from pulse generator 22. Inorder to re-distribute the secondary electrons emitted by the storagesurface over the surface in a substantially even manner, the amplitudesof the negative pulses applied to the main collector electrode 17 andthe subsidiary collector electrode 21 are different and this may be arranged by providing variable resistors 23, 24 in the lead from the pulsegenerator 22 and taking connections from the electrode 17 and 21 tothese resistors so that the amplitude of the separate pulses may bevaried at will. The necessary synchronous relationship betweengenerators 16, 20 and 22 is schematically illustrated by showing saidgenerators joined together in the drawing.

It will be understood that the pulse generators 20 and 22 are connectedin circuit with the vertical deflection generator 16 so that the pulsesto the light source 19 and to the electrodes 17 and 21 are producedduring the frame flyback period as required, but these circuitconnections are not shown on the drawings so as to reduce complicationthereof.

In Fig. 2, the arrangement is generally the same as in Fig. 1, andtherefore like parts are shown with like reference numerals. However,instead of providing a main collector electrode 17 and a subsidiarycollector electrode 21, a single collector electrode 25 is shown whichis of annular form and located in front of the charge storage surface 4and is specially shaped with a flared surface facing towards the storagesurface so as to produce a field in the vicinity of the charge storagesurface so as to influence electrostatically the re-distribution of thesecondary electrons in a substantially even manner over the chargestorage surface. The actual shape of this collector electrode 25 maytake several forms, and apart from the shape shown it may, for example,be arranged as a section of a cone.

It will be apparent that although the invention has been particularlydescribed in connection with tubes of the image iconoscope type, yetnevertheless it can equally well be applied to otherhigh-velocity-scanned storage type tubes such as normal iconoscopes.

I claim:

1. A television pick-up tube arrangement of the kind having a pick-uptube of the charge-storage type employing high-velocity scanning of aninsulated charge-storage surface, and a collector electrode to collectsecondary electrons emitted by said charge-storage surface during saidscanning, and in which periodically during the flyback periods of thescanning beam and preferably during the frame flyback periods saidcharge-storage surface is submitted to the simultaneous and combinedactions of an electron irradiation causing said storage surface to emitelectrons and of a field causing the emitted electrons to return to saidstorage surface so as to cause said storage surface to be chargednegatively relatively to its normal equilibrium potential, characterizedby the provision of field-modifying electrode means located adjacent andin front of said charge-storage surface rendering the field between saidstorage surface and said collector electrode substantially uniform toeffect the redistribution of the secondary electrons over the storagesurface in a substantially even manner.

2. A television pick-up tube arrangement as claimed in claim 1 in whichsaid field-modifying electrode means and said collector electrode arecombined into one structural element of substantially annular formarranged round the inside walls of the tube and which is flaredoutwardly towards the said charge-storage surface.

3. A television pick-up tube arrangement of the kind having a pick-uptube of the charge-storage type employing high-velocity scanning of aninsulated charge-storage surface, and a collector electrode to collectsecondary electrons emitted by said charge-storage surface during saidscanning, and in which periodically during the flyback periods of thescannning beam and preferably during the frame flyback periods saidcharge-storage surface is submitted to the simultaneous and combinedactions of an electron irradiation causing said storage surface to emitelectrons and of a field causing the emitted electrons to return to saidstorage surface so as to cause said storage surface to be chargednegatively relatively to its normal equilibrium potential, characterisedin that said collector electrode comprises a plurality of discretesections, and in that means are provided for applying negative voltagepulses of differing amplitude to the various sections, so as to effect asubstantially even redistribution of secondary electrons over saidstorage surface.

4. An arrangement as claimed in claim 3, in which said collectorelectrode has two sections, both of annular form and arranged inaxially-spaced relationship around the inside walls of the tube on theside of the charge storage surface that is scanned by the scanning beam.

5. An arrangement as claimed in claim 4, and comprising further anegative pulse generator, means for connecting said collector electrodesections to said generator and a resistor in each of said connectingmeans, said resistors having different values.

6. An arrangement as claimed in claim 4 and comprising further anegative pulse generator, means for connecting said collector electrodesections to said generator, and a variable resistor in each of saidconnecting means.

7. Television pick-up tube apparatus ofthe kind comprising a televisionpick-up tube of the high-velocityscanned image iconoscope type that hasa photo-cathode and an insulated charge-storage surface between which isarranged a collector electrode, and means for illuminating saidphoto-cathode with a pulse of diffuse light during the frame flybackperiods of operation of said tube, characterized in that said collectorelectrode comprises two discrete portions and in that means are providedfor applying to said portions of said collector electrode negativepulses of diifering amplitude also during said frame flyback periods.

8. Television pick-up tube apparatus of the kind comprising a televisionpick-up tube of the high-velocityscanned image iconoscope type that hasa photo-cathode and an insulated charge-storage surface between which isarranged a collector electrode, a diffuse light source located outsidesaid tube for illumination of said photo- -cathode, and a pulsegenerator connected to said light source for pulsing said light sourceon during the frameflyback periods of operation of said tube,characterised in that said collector electrode comprises two discreteportions, in that two resistors of different values are located outsidesaid tube connected respectively by one of their ends to said collectorelectrode portions, and in that a generator of negative pulses isconnected commonly to the other ends of said resistors, said generatorbeing operative to supply negative pulses to said collector electrodeportions via said resistors during only the said frame flyback periods.

9. Television pick-up tube apparatus as claimed in claim 8, in whichsaid resistors are variable resistors.

References Cited in the file of this patent UNITED STATES PATENTS2,433,941 Weimer Ian. 6, 1948 2,533,381 Levy Dec. 12, 1950 2,651,674Theile Sept. 8, 1953 2,733,292 Cope et al Jan. 31, 1956

